Missing at high RPM's

For the last couple weeks my car has been breaking up at high RPM's. I have checked the MSD ignition, the plug wires, changed the fuel pump and plugs and no change. It's almost like it's either electrical or fuel. This has me stumped. It ran perfect before. It's like it runs out of power or something is holding it back. I usually shift at 6200 and sometimes it's hard to get it past 5500 in 3rd gear. Any suggestions are greatly appreciated!!

Fred B